The 5-minute rate of uptake of glucose and 2-deoxyglucose is sharply enhanced by incubation of cell monolayers in a glucose-free medium for several hours. The mechanism of enhancement is not clearly resolved but the synthesis of both RNA and protein is required to achieve the "derepression". Glucose, 2-deoxyglucose, mannose, fructose, and glucosamine block expansion whereas galactose, other hexoses and a wide variety of pentoses and trioses do not. Indeed, pyruvate has a supplemental stimulatory effect. Insulin promotes uptake in "starved" or partially "starved" cells; however, the insulin and pyruvate effects are not additive. The effect of starvation on insulin receptors and the flow of labeled glucose will be studied.